title: Anion dependent redox changes in iron bis-terdentate nitroxide {NNO} chelates.
abstract: The reaction of [Fe(II)(BF(4))(2)]·6H(2)O with the nitroxide radical, 4,4-dimethyl-2,2-di(2-pyridyl) oxazolidine-N-oxide (L(•)), produces the mononuclear transition metal complex [Fe(II)(L(•))(2)](BF(4))(2) (1) which has been investigated using temperature dependent susceptibility, Mössbauer spectroscopy, electrochemistry, density functional theory (DFT) calculations, and X-ray structure analysis. Single crystal X-ray diffraction analysis and Mössbauer measurements reveal an octahedral low spin Fe(2+) environment where the pyridyl donors from L(•) coordinate equatorially while the oxygen containing the radical from L(•) coordinates axially forming a linear O(•)··Fe(II)··O(•) arrangement. Magnetic susceptibility measurements show a strong radical-radical intramolecular antiferromagnetic interaction mediated by the diamagnetic Fe(2+) center. This is supported by DFT calculations which show a mutual spatial overlap of 0.24 and a spin density population analysis which highlights the antiparallel spin alignment between the two ligands. Similarly the monocationic complex [Fe(III)(L(-))(2)](BPh(4))·0.5H(2)O (2) has been fully characterized with Fe-ligand and N-O bond length changes in the X-ray structure analysis, magnetic measurements revealing a Curie-like S = 1/2 ground state, electron paramagnetic resonance (EPR) spectra, DFT calculations, and electrochemistry measurements all consistent with assignment of Fe in the (III) state and both ligands in the L(-) form. 2 is formed by a rare, reductively induced oxidation of the Fe center, and all physical data are self-consistent. The electrochemical studies were undertaken for both 1 and 2, thus allowing common Fe-ligand redox intermediates to be identified and the results interpreted in terms of square reaction schemes.
authors.affiliation: School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
authors.forename: Ian A
authors.initials: IA
authors.lastname: Gass
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Gartshore
authors.forename: David W
authors.initials: DW
authors.lastname: Lupton
authors.forename: Boujemaa
authors.initials: B
authors.lastname: Moubaraki
authors.forename: Ayman
authors.initials: A
authors.lastname: Nafady
authors.forename: Alan M
authors.initials: AM
authors.lastname: Bond
authors.forename: John F
authors.initials: JF
authors.lastname: Boas
authors.forename: John D
authors.initials: JD
authors.lastname: Cashion
authors.forename: Carsten
authors.initials: C
authors.lastname: Milsmann
authors.forename: Karl
authors.initials: K
authors.lastname: Wieghardt
authors.forename: Keith S
authors.initials: KS
authors.lastname: Murray
mesh_terms: D000838:Anions / Q000737:chemistry; D002614:Chelating Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009589:Nitrogen Oxides / Q000737:chemistry*; D010084:Oxidation-Reduction; D011789:Quantum Theory
chemical_list: D000838:Anions; D002614:Chelating Agents; D005290:Ferric Compounds; D005296:Ferrous Compounds; D008024:Ligands; D009589:Nitrogen Oxides